This invention relates to a hard magnetic bubble domain analog multiplier having an improved linear response of bubble domain propagating velocities produced by the product of two propagation control magnetic fields. More particularly, the invention relates to a hard magnetic bubble domain analog multiplier having repulsive boundaries defining a propagating channel perpendicular to the direction of a driving field gradient established by one of the two control fields.
Prior magnetic domain analog computational arrangements are known utilizing drive control magnetic fields for propagating single wall magnetic domains or bubble domains with predetermined responses. The velocity and direction of bubble domains are controlled in a domain multiplier computational arrangement by the combined response to at least two drive control fields. Computational inputs are formed by electrical signals related to quantities to be computed upon. These electrical input signals control or produce the drive control magnetic fields directed into a predetermined magnetic bubble domain propagating path or channel. Examples of analog bubble domain computational arrangements are disclosed in the above cross-referenced Pat. No. 3,845,478 and also in U.S. Pat. No. 3,825,910 issued July 23, 1974 also assigned to the assignee of this invention.
Magnetic bubble domains are propagated in accordance with the disclosure of U.S. Pat. No. 3,825,910 by a self-induced magnetic drive field established when a bubble domain is moved above a semiconductor drive layer having a uniform current density. Various analog computational arrangements are described in the aforementioned patent with a bubble domain being propagated by a field carried with the domain. In one arrangement, an additional control magnetic field is applied to a predetermined propagating channel so that the velocity of the magnetic bubble domain is proportional to the product of the controlled magnetic field and the level of the uniform current density layer producing the induced field. In the latter arrangement, the net displacement of the bubble domain produces a computational output proportional to the product of two quantities controlling the control magnetic field and the uniform drive layer current. Some limitations are found in the device just described in the difficulty of obtaining semiconductor materials having proper Hall effect characteristics. The complex interactions of magnetic fields including those including the Hall effect field interactions produce some difficulty in controlling the resultant bubble domain movement. It is noted that the basic mode of propagating bubble domains in the above-described device differs from that of the present invention.
The present invention is more directly related to and is an improvement of the bubble domain computational arrangement disclosed in the above cross-referenced U.S. Pat. No. 3,845,478. The arrangement disclosed propagates magnetic bubble domains in response to the product of two drive control magnetic fields controlled by two alternating current input signals. The first drive control field is effective to modulate the bubble domain size or diameter and the second drive control field produces a modulated field gradient applied across the bubble domain. Bubble domains are driven at an average velocity associated with a net displacement proportional to the product of the variations in the domain size and the level of the field gradient. Input signals, proportional to voltage and current components of an electric power consumption quantity to be computed, are effective to separately control the first and second drive control fields. The net velocity of the magnetic bubble domain is a computed measurement of electric power. Accordingly, the detected displacement of the magnetic bubble domain provides an indication of the time integral of the multiplied voltage and current quantities and thus a computed measure of electrical energy.
The direction of the magnetic bubble domain net displacement in the U.S. Pat. No. 3,845,478 is along the direction of the controlled magnetic field gradient with the magnetic bubble domains being soft or normal magnetic bubble domains. The described propagated movement is oscillatory with reciprocating motion rather than with a cyclical orbital motion produced in the present invention. It has been observed that in the operation of the propagating device of the aforementioned patent, the controlled field gradient may produce substantial modulation of the magnetic bubble domain diameter in addition to the variations in the bubble domain diameter produced by the size modulating field. Since the domain size is directly interrelated to associated driving field gradient, the dynamic range of input signals is sometimes limited. Undesirably, the magnetic bubble domain is propagated so that its velocity is not directly related to the product of the two drive control fields. This occurs since the two fields do not independently modulate the domain diameter and field gradient. The domain diameter variations due to the controlled field gradient are referred to as a self-multiplication effect of the magnetic bubble. Accordingly, it is desirable to avoid self-multiplication, drift components in the net bubble domain displacement, and other effects producing non-linear response in a magnetic bubble domain analog multiplier device and especially those effects causing unacceptable mixing of the two drive control field contributions to domain computational movement. To improve these undesired effects, the present invention utilizes the propagating characteristics of hard magnetic domains having what is believed a more complex magnetically defined wall structure to provide an oscillatory cyclical motion that produces a net displacement more linearly responsive to the product of two propagating control fields.